The present disclosure relates generally relates to the field of obstacle detection by an aircraft.
A growing share of CFIT (Controlled Flight Into Terrain) accidents over the last twenty years, both in civil and military aviation, has led to the development of systems for warning an aircraft's flight crew of a risk of collision with the ground. This trend has become more pronounced in the last ten years, with the requirement that civil aircrafts carrying more than fifteen people have TAWS systems (Terrain Awareness and Warning System). These TAWS systems predict the layout of the ground from the aircraft using flight computers, project that layout on a terrain elevation map resulting from an onboard database, and emit sound and visual alarms for risks of collision with the ground each time the anticipated trajectory collides with the elevation map.
In a TAWS system, the margin used to determine whether an aircraft risks colliding with an obstacle is a fixed margin. It is chosen to protect aircrafts moving at high speeds. As a result, when an aircraft moves at a low speed, TAWS systems generate many false alarms. Furthermore, TAWS systems based on an elevation database cannot protect the aircraft from risks of collision with obstacles in the actual environment, for example cables, pylons, towers, cranes, etc. In fact, these obstacles may not be exhaustively inventoried in a shared database updated worldwide.
In a TAWS system, obstacle detection is generally done by entering, a priori, a certain amount of obstacle information into a TAWS database in the form of reference points (generally in latitude/longitude coordinates), with an imposed geometry (cylinder, square) and an elevation value. This obstacle data is interpreted by the TAWS system as a local over-elevation of the terrain locally around the point. However, the terrain elevation database of a TAWS system may be broken down into rectangular cells having low resolution (approximately 3 arc seconds). Since the precision of the elevation detection done by the TAWS system depends on the size of the cell in which the reference point of the obstacle is located, the false alarm rate (because the system is conservative and prefers to provide alerts) may be high for obstacles.
Furthermore, in a TAWS system, the detection of potential collisions with obstacles is based on the validity and precision of the information recorded in the obstacle database. When this data is incorrect or obsolete, in particular in an environment having non-inventoried temporary obstacles, the effectiveness of such a collision detection system is reduced. A TAWS system may also be poorly adapted to aircrafts traveling at low speeds, as it is impossible to project their trajectories at low speeds. Furthermore, in that mode, the influence of wind on the aircraft becomes preponderant in assessing the danger relative to the obstacles and the TAWS system does not meet this need.